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Prerequisites for Configuring a Basic BGP Network

Before configuring basic BGP tasks you should be familiar with the "Cisco BGP Overview" module.

Restrictions for Configuring a Basic BGP Network

A router that runs Cisco IOS software can be configured to run only one BGP routing process and to be a member of only one BGP autonomous system. However, a BGP routing process and autonomous system can support multiple address family configurations.

Information About Configuring a Basic BGP Network

To configure a basic BGP network you should understand the following concepts:

BGP is mainly used to connect a local network to an external network to gain access to the Internet or to connect to other organizations. When connecting to an external organization, external BGP (eBGP) peering sessions are created. Although BGP is referred to as an exterior gateway protocol (EGP) many networks within an organization are becoming so complex that BGP can be used to simplify the internal network used within the organization. BGP peers within the same organization exchange routing information through internal BGP (iBGP) peering sessions.

Note BGP requires more configuration than other routing protocols and the effects of any configuration changes must be fully understood. Incorrect configuration can create routing loops and negatively impact normal network operation.

BGP-Speaker and Peer Relationships

A BGP-speaking router does not discover another BGP-speaking device automatically. A network administrator usually manually configures the relationships between BGP-speaking routers. A peer device is a BGP-speaking router that has an active TCP connection to another BGP-speaking device. This relationship between BGP devices is often referred to as a neighbor but, as this can imply the idea that the BGP devices are directly connected with no other router in between, the term neighbor will be avoided whenever possible in this document. A BGP speaker is the local router and a peer is any other BGP-speaking network device.

When a TCP connection is established between peers, each BGP peer initially exchanges all its routes—the complete BGP routing table—with the other peer. After this initial exchange only incremental updates are sent when there has been a topology change in the network, or when a routing policy has been implemented or modified. In the periods of inactivity between these updates, peers exchange special messages called keepalives.

A BGP autonomous system is a network controlled by a single technical administration entity. Peer routers are called external peers when they are in different autonomous systems and internal peers when they are in the same autonomous system. Usually, external peers are adjacent and share a subnet; internal peers may be anywhere in the same autonomous system.

BGP Peer Session Establishment

When a BGP routing process establishes a peering session with a peer it goes through the following state changes:

•Idle—Initial state the BGP routing process enters when the routing process is enabled or when the router is reset. In this state, the router waits for a start event, such as a peering configuration with a remote peer. After the router receives a TCP connection request from a remote peer, the router initiates another start event to wait for a timer before starting a TCP connection to a remote peer. If the router is reset then the peer is reset and the BGP routing process returns to the Idle state.

•Connect—The BGP routing process detects that a peer is trying to establish a TCP session with the local BGP speaker.

•Active—In this state, the BGP routing process tries to establish a TCP session with a peer router using the ConnectRetry timer. Start events are ignored while the BGP routing process is in the Active state. If the BGP routing process is reconfigured or if an error occurs, the BGP routing process will release system resources and return to an Idle state.

•OpenSent—The TCP connection is established and the BGP routing process sends an OPEN message to the remote peer, and transitions to the OpenSent state. The BGP routing process can receive other OPEN messages in this state. If the connection fails, the BGP routing process transitions to the Active state.

•OpenReceive—The BGP routing process receives the OPEN message from the remote peer and waits for an initial keepalive message from the remote peer. When a keepalive message is received, the BGP routing process transitions to the Established state. If a notification message is received, the BGP routing process transitions to the Idle state. If an error or configuration change occurs that affects the peering session, the BGP routing process sends a notification message with the Finite State Machine (FSM) error code and then transitions to the Idle state.

•Established—The initial keepalive is received from the remote peer. Peering is now established with the remote neighbor and the BGP routing process starts exchanging update message with the remote peer. The hold timer restarts when an update or keepalive message is received. If the BGP process receives an error notification, it will transition to the Idle state.

Cisco Implementation of BGP Global and Address Family Configuration Commands

The address family model for configuring BGP is based on splitting apart the configuration for each address family. All commands that are independent of the address family are grouped together at the beginning (highest level) of the configuration, and these are followed by separate submodes for commands specific to each address family (with the exception that commands relating to IPv4 unicast can also be entered at the beginning of the configuration). When a network operator configures BGP, the flow of BGP configuration categories is represented by the following bullets in order:

•Global configuration—configuration that is applied to BGP in general, rather than to specific neighbors. For example, the network, redistribute, and bgp bestpath commands.

•Address family-dependent configuration—configuration that applies to a specific address family such as policy on an individual neighbor.

The relationship between BGP global and BGP address family-dependent configuration categories is shown in Table 1.

Table 1 Relationships between BGP Configuration Categories

BGP Configuration Category

Configuration Sets Within Category

Global address family-independent

One set of global address family-independent configurations

Address family-dependent

One set of global address family-dependent configurations per address family

Note Address family configuration must be entered within the address family submode to which it applies.

The following is an example of BGP configuration statements showing the grouping of global address family-independent and address family-dependent commands.

router bgp <AS>

! AF independent part

neighbor <ip-address> <command> ! Session config; AF independent !

address-family ipv4 unicast

! AF dependant part

neighbor <ip-address> <command> ! Policy config; AF dependant

exit-address-family !

address-family ipv4 multicast

! AF dependant part

neighbor <ip-address> <command> ! Policy config; AF dependant

exit-address-family !

address-family ipv4 unicast vrf <vrf-name>

! VRF specific AS independent commands

! VRF specific AS dependant commands

neighbor <ip-address> <command> ! Session config; AF independent

neighbor <ip-address> <command> ! Policy config; AF dependant

exit-address-family !

The following example shows actual BGP commands that match the BGP configuration statements in the previous example:

router bgp 45000

router-id 172.17.1.99

bgp log-neighbor-changes

neighbor 192.168.1.2 remote-as 40000

neighbor 192.168.3.2 remote-as 50000

address-family ipv4 unicast

neighbor 192.168.1.2 activate

network 172.17.1.0 mask 255.255.255.0

exit-address-family

address-family ipv4 multicast

neighbor 192.168.3.2 activate

neighbor 192.168.3.2 advertisement-interval 25

network 172.16.1.0 mask 255.255.255.0

exit-address-family

address-family ipv4 vrf vpn1

neighbor 192.168.3.2 activate

network 172.21.1.0 mask 255.255.255.0

exit-address-family

In Cisco IOS Releases 12.0(22)S, 12.2(15)T, and later releases the bgp upgrade-cli command simplifies the migration of BGP networks and existing configurations from the network layer reachability information (NLRI) format to the address family format. Network operators can configure commands in the address family identifier (AFI) format and save these command configurations to existing NLRI formatted configurations. The BGP hybrid command-line interface (CLI) does not add support for complete AFI and NLRI integration because of the limitations of the NLRI format. For complete support of AFI commands and features, we recommend upgrading existing NLRI configurations with the bgp upgrade-cli command. For a configuration example of migrating BGP configurations from the NLRI format to the address family format, see the "NLRI to AFI Configuration: Example" section.

BGP Session Reset

Whenever there is a change in the routing policy due to a configuration change, BGP peering sessions must be reset using the clear ip bgp command. Cisco IOS software support the following three mechanisms to reset BGP peering sessions:

•Hard reset—A hard reset tears down the specified peering sessions including the TCP connection and deletes routes coming from the specified peer.

•Soft reset—A soft reset uses stored prefix information to reconfigure and activate BGP routing tables without tearing down existing peering sessions. Soft reconfiguration uses stored update information, at the cost of additional memory for storing the updates, to allow you to apply new BGP policy without disrupting the network. Soft reconfiguration can be configured for inbound or outbound sessions.

•Dynamic inbound soft reset—The route refresh capability, as defined in RFC 2918, allows the local router to reset inbound routing tables dynamically by exchanging route refresh requests to supporting peers. The route refresh capability does not store update information locally for non disruptive policy changes. It instead relies on dynamic exchange with supporting peers. Route refresh must first be advertised through BGP capability negotiation between peers. All BGP routers must support the route refresh capability.

To determine if a BGP router supports this capability, use the show ip bgp neighbors command. The following message is displayed in the output when the router supports the route refresh capability:

Received route refresh capability from peer.

In Cisco IOS Release 12.3(14)T the bgp soft-reconfig-backup command was introduced to configure BGP to perform inbound soft reconfiguration for peers that do not support the route refresh capability. The configuration of this command allows you to configure BGP to store updates (soft reconfiguration) only as necessary. Peers that support the route refresh capability are unaffected by the configuration of this command.

BGP Route Aggregation

BGP peers store and exchange routing information and the amount of routing information increases as more BGP speakers are configured. The use of route aggregation reduces the amount of information involved. Aggregation is the process of combining the attributes of several different routes so that only a single route is advertised. Aggregate prefixes use the classless interdomain routing (CIDR) principle to combine contiguous networks into one classless set of IP addresses that can be summarized in routing tables. Fewer routes now need to be advertised.

Two methods are available in BGP to implement route aggregation. You can redistribute an aggregated route into BGP or you can use a form of conditional aggregation. Basic route redistribution involves creating an aggregate route and then redistributing the routes into BGP. Conditional aggregation involves creating an aggregate route and then advertising or suppressing the advertising of certain routes on the basis of route maps, autonomous system set path (AS-SET) information, or summary information.

In Cisco IOS Release 12.2(25)S, and 12.2(33)SXH, the bgp suppress-inactive command was introduced to configure BGP to not advertise inactive routes to any BGP peer. A BGP routing process can advertise routes that are not installed in the routing information database (RIB) to BGP peers by default. A route that is not installed into the RIB is an inactive route. Inactive route advertisement can occur, for example, when routes are advertised through common route aggregation. Inactive route advertisements can be suppressed to provide more consistent data forwarding.

BGP Peer Groups

Often, in a BGP network, many neighbors are configured with the same update policies (that is, the same outbound route maps, distribute lists, filter lists, update source, and so on). Neighbors with the same update policies can be grouped into BGP peer groups to simplify configuration and, more importantly, to make configuration updates more efficient. When you have many peers, this approach is highly recommended.

Peer Groups and BGP Update Messages

In Cisco IOS software releases prior to Release 12.0(24)S, 12.2(18)S, or 12.3(4)T, BGP update messages were grouped based on peer group configurations. This method of grouping neighbors for BGP update message generation reduced the amount of system processing resources needed to scan the routing table. This method, however, had the following limitations:

•All neighbors that shared peer group configuration also had to share outbound routing policies.

•All neighbors had to belong to the same peer group and address family. Neighbors configured in different address families could not belong to different peer groups.

These limitations existed to balance optimal update generation and replication against peer group configuration. These limitations could cause the network operator to configure smaller peer groups, which reduced the efficiency of update message generation and limited the scalability of neighbor configuration.

BGP Update Group

The introduction of the BGP (dynamic) update group in Cisco IOS Releases 12.0(24)S, 12.2(18)S, 12.3(4)T, or 12.2(27)SBC provides a different type of BGP peer grouping from existing BGP peer groups. Existing peer groups are not affected but peers with the same outbound policy configured that are not members of a current peer group can be grouped into an update group. The members of this update group will use the same update generation engine. When BGP update groups are configured an algorithm dynamically calculates the BGP update group membership based on outbound policies. Optimal BGP update message generation occurs automatically and independently. BGP neighbor configuration is no longer restricted by outbound routing policies, and update groups can belong to different address families.

Peer Templates

To address some of the limitations of peer groups such as configuration management, BGP peer templates were introduced to support the BGP update group configuration.

A peer template is a configuration pattern that can be applied to neighbors that share policies. Peer templates are reusable and support inheritance, which allows the network operator to group and apply distinct neighbor configurations for BGP neighbors that share policies. Peer templates also allow the network operator to define very complex configuration patterns through the capability of a peer template to inherit a configuration from another peer template.

There are two types of peer templates:

•Peer session templates are used to group and apply the configuration of general session commands that are common to all address family and NLRI configuration modes.

•Peer policy templates are used to group and apply the configuration of commands that are applied within specific address families and NLRI configuration modes.

Peer templates improve the flexibility and enhance the capability of neighbor configuration. Peer templates also provide an alternative to peer group configuration and overcome some limitations of peer groups. BGP peer routers using peer templates also benefit from automatic update group configuration. With the configuration of the BGP peer templates and the support of the BGP dynamic update peer groups, the network operator no longer needs to configure peer groups in BGP and the network can benefit from improved configuration flexibility and faster convergence.

Note The configuration of BGP peer templates does not conflict with or restrict peer group configuration and peer groups are still supported in Cisco IOS Releases that support BGP peer templates. However, a BGP neighbor cannot be configured to work with both peer groups and peer templates. A BGP neighbor can be configured to belong only to a peer group or to inherit policies from peer templates.

How to Configure a Basic BGP Network

Configuring a basic BGP network consists of a few required tasks and many optional tasks. A BGP routing process must be configured and BGP peers must be configured, preferably using the address family configuration model. If the BGP peers are part of a VPN network then the BGP peers must be configured using the IPv4 VRF address family task. The other tasks in the following list are optional:

Configuring a BGP Routing Process

Perform this task to configure a BGP routing process. You must perform the required steps at least once to enable BGP. The optional steps here allow you to configure additional features in your BGP network. Several of the features, such as logging neighbor resets and immediate reset of a peer when its link goes down, are enabled by default but are presented here to enhance your understanding of how your BGP network operates.

Note A router that runs Cisco IOS software can be configured to run only one BGP routing process and to be a member of only one BGP autonomous system. However, a BGP routing process and autonomous system can support multiple concurrent BGP address family and subaddress family configurations.

The configuration in this task is done at Router A in Figure 1 and would need to be repeated with appropriate changes to the IP addresses (for example, at Router B) to fully achieve a BGP process between the two routers. No address family is configured here for the BGP routing process so routing information for the IPv4 unicast address family is advertised by default.

Figure 1 BGP Topology with Two Autonomous Systems

BGP Router ID

BGP uses a router ID to identify BGP-speaking peers. The BGP router ID is 32-bit value that is often represented by an IPv4 address. By default, the Cisco IOS software sets the router ID to the IPv4 address of a loopback interface on the router. If no loopback interface is configured on the router, then the software chooses the highest IPv4 address configured to a physical interface on the router to represent the BGP router ID. The BGP router ID must be unique to the BGP peers in a network.

•Use the keepalive argument to specify the frequency, in seconds, with which the software sends keepalive messages to its BGP peer. By default, the keepalive timer is set to 60 seconds.

•Use the holdtime argument to specify the interval, in seconds, after not receiving a keepalive message that the software declares a BGP peer dead. By default, the holdtime timer is set to 180 seconds.

Step 7

bgp fast-external-fallover

Example:

Router(config-router)# bgp fast-external-fallover

(Optional) Enables the automatic resetting of BGP sessions.

•By default, the BGP sessions of any directly adjacent external peers are reset if the link used to reach them goes down.

•Use this command for troubleshooting network connectivity problems and measuring network stability. Unexpected neighbor resets might indicate high error rates or high packet loss in the network and should be investigated.

Examples

The following sample output from the show ip bgp command shows the BGP routing table for Router A in Figure 1 after this task has been configured on Router A. You can see an entry for the network 10.1.1.0 that is local to this autonomous system.

Troubleshooting Tips

Use the ping command to check basic network connectivity between the BGP routers.

Configuring a BGP Peer

Perform this task to configure BGP between two IPv4 routers (peers). The address family configured here is the default IPv4 unicast address family and the configuration is done at Router A in Figure 1. Remember to perform this task for any neighbor routers that are to be BGP peers.

Prerequisites

Restrictions

By default, neighbors that are defined using the neighbor remote-as command in router configuration mode exchange only IPv4 unicast address prefixes. To exchange other address prefix types, such as IPv6 prefixes, neighbors must also be activated using the neighbor activate command in address family configuration mode for the other prefix types, such as IPv6 prefixes.

SUMMARY STEPS

1. enable

2. configureterminal

3. router bgp autonomous-system-number

4. neighbor ip-address remote-as autonomous-system-number

5. address-family ipv4 [unicast | multicast | vrf vrf-name]

6. neighbor ip-address activate

7. end

8. show ip bgp [network][network-mask]

9. show ip bgp neighbors [neighbor-address]

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Router> enable

Enables privileged EXEC mode.

•Enter your password if prompted.

Step 2

configureterminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3

router bgp autonomous-system-number

Example:

Router(config)# router bgp 40000

Enters router configuration mode for the specified routing process.

Step 4

neighbor ip-address remote-as autonomous-system-number

Example:

Router(config-router)# neighbor 192.168.1.1 remote-as 45000

Adds the IP address of the neighbor in the specified autonomous system to the IPv4 multiprotocol BGP neighbor table of the local router.

Step 5

address-family ipv4 [unicast | multicast | vrf vrf-name]

Example:

Router(config-router)# address-family ipv4 unicast

Specifies the IPv4 address family and enters address family configuration mode.

•The unicast keyword specifies the IPv4 unicast address family. By default, the router is placed in configuration mode for the IPv4 unicast address family if the unicast keyword is not specified with the address-family ipv4 command.

•The multicast keyword specifies IPv4 multicast address prefixes.

•The vrf keyword and vrf-name argument specify the name of the virtual routing and forwarding (VRF) instance to associate with subsequent IPv4 address family configuration mode commands.

Step 6

neighbor ip-address activate

Example:

Router(config-router-af)# neighbor 192.168.1.1 activate

Enables the neighbor to exchange prefixes for the IPv4 unicast address family with the local router.

Examples

The following sample output from the show ip bgp command shows the BGP routing table for Router A in Figure 1 after this task has been configured on Router A and Router B. You can now see an entry for the network 172.17.1.0 in autonomous system 45000.

The following sample output from the show ip bgp neighbors command shows information about the TCP and BGP connections to the BGP neighbor 192.168.1.1 of Router A in Figure 1 after this task has been configured on Router A:

BGP neighbor is 192.168.1.1, remote AS 45000, external link

BGP version 4, remote router ID 172.17.1.99

BGP state = Established, up for 00:06:55

Last read 00:00:15, last write 00:00:15, hold time is 120, keepalive intervals

What To Do Next

Configuring a BGP Peer for the IPv4 VRF Address Family

Perform this optional task to configure BGP between two IPv4 routers (peers) that must exchange IPv4 VRF information because they exist in a VPN. The address family configured here is the IPv4 VRF address family and the configuration is done at Router B in Figure 2 with the neighbor 192.168.3.2 at Router E in autonomous system 50000. Remember to perform this task for any neighbor routers that are to be BGP IPv4 VRF address family peers.

Note This task does not show the complete configuration required for VPN routing. For some complete example configurations see the "Additional References" section.

•Use the both keyword to import both import and export routing information to the target VPN extended community.

•Use the route-target-ext-community argument to add the route target extended community attributes to the VRF's list of import, export, or both (import and export) route target extended communities.

Step 6

exit

Example:

Router(config-vrf)# exit

Exits VRF configuration mode and enters global configuration mode.

Step 7

router bgp autonomous-system-number

Example:

Router(config)# router bgp 45000

Enters router configuration mode for the specified routing process.

Step 8

address-family ipv4 [unicast | multicast | vrf vrf-name]

Example:

Router(config-router)# address-family ipv4 vrf vpn1

Specifies the IPv4 address family and enters address family configuration mode.

•Use the unicast keyword to specify the IPv4 unicast address family. By default, the router is placed in configuration mode for the IPv4 unicast address family if the unicast keyword is not specified with the address-family ipv4 command.

•Use the maximum argument to specify the maximum number of prefixes allowed from the specified neighbor. The number of prefixes that can be configured is limited only by the available system resources on a router.

•Use the threshold argument to specify an integer representing a percentage of the maximum prefix limit at which the router starts to generate a warning message.

•Use the warning-only keyword to allow the router to generate a log message when the maximum prefix limit is exceeded, instead of terminating the peering session.

Step 11

neighbor ip-address activate

Example:

Router(config-router-af)# neighbor 192.168.3.2 activate

Enables the neighbor to exchange prefixes for the IPv4 VRF address family with the local router.

Troubleshooting Tips

Use the ping command to verify basic network connectivity between the BGP routers and use the show ip vrf command to verify that the VRF instance has been created.

Customizing a BGP Peer

Perform this task to customize your BGP peers. Although many of the steps in this task are optional, this task demonstrates how the neighbor and address family configuration command relationships work. Using the example of the IPv4 multicast address family, neighbor address family-independent commands are configured before the IPv4 multicast address family is configured. Commands that are address family-dependent are then configured and the exit address-family command is shown. An optional step shows how to disable a neighbor.

The configuration in this task is done at Router B in Figure 3 and would need to be repeated with appropriate changes to the IP addresses, for example, at Router E to fully configure a BGP process between the two routers.

Figure 3 BGP Peer Topology

Restrictions

By default, neighbors that are defined using the neighbor remote-as command in router configuration mode exchange only IPv4 unicast address prefixes. To exchange other address prefix types, such as IPv6 prefixes, neighbors must also be activated using the neighbor activate command in address family configuration mode for the other prefix types, such as IPv6 prefixes.

Note Routing information for the IPv4 unicast address family is advertised by default for each BGP routing session configured with the neighbor remote-as router configuration command unless you configure the no bgp default ipv4-unicast router configuration command before configuring the neighbor remote-as command. Existing neighbor configurations are not affected.

Adds the IP address of the neighbor in the specified autonomous system to the IPv4 multiprotocol BGP neighbor table of the local router.

Step 6

neighbor {ip-address | peer-group-name}description text

Example:

Router(config-router)# neighbor 192.168.3.2 description finance

(Optional) Associates a text description with the specified neighbor.

Step 7

address-family ipv4 [unicast | multicast | vrf vrf-name]

Example:

Router(config-router)# address-family ipv4 multicast

Specifies the IPv4 address family and enters address family configuration mode.

•The unicast keyword specifies the IPv4 unicast address family. By default, the router is placed in configuration mode for the IPv4 unicast address family if the unicast keyword is not specified with the address-family ipv4 command.

•The multicast keyword specifies IPv4 multicast address prefixes.

•The vrf keyword and vrf-name argument specify the name of the VRF instance to associate with subsequent IPv4 address family configuration mode commands.

Step 8

network network-number[masknetwork-mask][route-maproute-map-name]

Example:

Router(config-router-af)# network 172.17.1.0 mask 255.255.255.0

(Optional) Specifies a network as local to this autonomous system and adds it to the BGP routing table.

•For exterior protocols the network command controls which networks are advertised. Interior protocols use the network command to determine where to send updates.

(Optional) Displays information about the TCP and BGP connections to neighbors.

Examples

The following sample output from the show ip bgp ipv4 multicast command shows BGP IPv4 multicast information for Router B in Figure 3 after this task has been configured on Router B and Router E. Note that the networks local to each router that were configured under IPv4 multicast address family appear in the output table.

The following partial sample output from the show ip bgp neighbors command for neighbor 192.168.3.2 shows general BGP information and specific BGP IPv4 multicast address family information about the neighbor. The command was entered on Router B in Figure 3 after this task has been configured on Router B and Router E.

BGP neighbor is 192.168.3.2, remote AS 50000, external link

Description: finance

BGP version 4, remote router ID 10.2.2.99

BGP state = Established, up for 01:48:27

Last read 00:00:26, last write 00:00:26, hold time is 120, keepalive intervals

Monitoring and Maintaining Basic BGP

The tasks in this section are concerned with the resetting and display of information about basic BGP processes and peer relationships. Once you have defined two routers to be BGP neighbors, they will form a BGP connection and exchange routing information. If you subsequently change a BGP filter, weight, distance, version, or timer, or make a similar configuration change, you may have to reset BGP connections for the configuration change to take effect.

Routing Policy Change Management

Routing policies for a peer include all the configurations for elements such as route map, distribute list, prefix list, and filter list that may impact inbound or outbound routing table updates. Whenever there is a change in the routing policy, the BGP session must be soft cleared, or soft reset, for the new policy to take effect. Performing inbound reset enables the new inbound policy configured on the router to take effect. Performing outbound reset causes the new local outbound policy configured on the router to take effect without resetting the BGP session. As a new set of updates is sent during outbound policy reset, a new inbound policy of the neighbor can also take effect. This means that after changing inbound policy you must do an inbound reset on the local router or an outbound reset on the peer router. Outbound policy changes require an outbound reset on the local router or an inbound reset on the peer router.

There are two types of reset, hard reset and soft reset. Table 2 lists their advantages and disadvantages.

Table 2 Advantages and Disadvantages of Hard and Soft Resets

Type of Reset

Advantages

Disadvantages

Hard reset

No memory overhead.

The prefixes in the BGP, IP, and Forwarding Information Base (FIB) tables provided by the neighbor are lost. Not recommended.

Outbound soft reset

No configuration, no storing of routing table updates.

Does not reset inbound routing table updates.

Dynamic inbound soft reset

Does not clear the BGP session and cache.

Does not require storing of routing table updates, and has no memory overhead.

Both BGP routers must support the route refresh capability (in Cisco IOS Release 12.1 and later releases).

Can be used when both BGP routers do not support the automatic route refresh capability.

In Cisco IOS Release 12.3(14)T the bgp soft-reconfig-backup command was introduced to configure inbound soft reconfiguration for peers that do not support the route refresh capability.

Requires preconfiguration.

Stores all received (inbound) routing policy updates without modification; is memory-intensive.

Recommended only when absolutely necessary, such as when both BGP routers do not support the automatic route refresh capability.

Note Does not reset outbound routing table updates.

Once you have defined two routers to be BGP neighbors, they will form a BGP connection and exchange routing information. If you subsequently change a BGP filter, weight, distance, version, or timer, or make a similar configuration change, you must reset BGP connections for the configuration change to take effect.

A soft reset updates the routing table for inbound and outbound routing updates. Cisco IOS Release 12.1 and later releases support soft reset without any prior configuration. This soft reset allows the dynamic exchange of route refresh requests and routing information between BGP routers, and the subsequent readvertisement of the respective outbound routing table. There are two types of soft reset:

•When soft reset is used to generate inbound updates from a neighbor, it is called dynamic inbound soft reset.

•When soft reset is used to send a new set of updates to a neighbor, it is called outbound soft reset.

To use soft reset without preconfiguration, both BGP peers must support the soft route refresh capability, which is advertised in the OPEN message sent when the peers establish a TCP session. Routers running Cisco IOS releases prior to Release 12.1 do not support the route refresh capability and must clear the BGP session using the neighbor soft-reconfiguration router configuration command. Clearing the BGP session in this way will have a negative impact upon network operations and should be used only as a last resort.

Perform this task to configure inbound soft reconfiguration using the bgp soft-reconfig-backup command for BGP peers that do not support the route refresh capability. BGP Peers that support the route refresh capability are unaffected by the configuration of this command.

9. Repeat Steps 6 through 8 for every peer that is to be configured with soft-reconfiguration inbound.

10. exit

11. route-map map-tag [permit|deny] [sequence-number]

12. set local-preference number-value

13. end

14. show ip bgp neighbors [neighbor-address]

15. show ip bgp [network][network-mask]

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Router> enable

Enables privileged EXEC mode.

•Enter your password if prompted.

Step 2

configureterminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3

router bgp autonomous-system-number

Example:

Router(config)# router bgp 45000

Enters router configuration mode for the specified routing process.

Step 4

bgp log-neighbor-changes

Example:

Router(config-router)# bgp log-neighbor-changes

Enables logging of BGP neighbor resets.

Step 5

bgp soft-reconfig-backup

Example:

Router(config-router)# bgp soft-reconfig-backup

Configures a BGP speaker to perform inbound soft reconfiguration for peers that do not support the route refresh capability.

•This command is used to configure BGP to perform inbound soft reconfiguration for peers that do not support the route refresh capability. The configuration of this command allows you to configure BGP to store updates (soft reconfiguration) only as necessary. Peers that support the route refresh capability are unaffected by the configuration of this command.

•All the updates received from this neighbor will be stored unmodified, regardless of the inbound policy. When inbound soft reconfiguration is done later, the stored information will be used to generate a new set of inbound updates.

Step 8

neighbor {ip-address | peer-group-name} route-map map-name {in | out}

Example:

Router(config-router)# neighbor 192.168.1.2 route-map LOCAL in

Applies a route map to incoming or outgoing routes.

•In this example, the route map named LOCAL will be applied to incoming routes.

Step 9

Repeat Steps 6 through 8 for every peer that is to be configured with soft-reconfiguration inbound.

—

Step 10

exit

Example:

Router(config-router)# exit

Exits router configuration mode and enters global configuration mode.

Step 11

route-map map-name [permit | deny][sequence-number]

Example:

Router(config)# route-map LOCAL permit 10

Configures a route map and enters route map configuration mode.

•In this example, a route map named LOCAL is created.

Step 12

set local-preference number-value

Example:

Router(config-route-map)# set local-preference 200

Specifies a preference value for the autonomous system path.

•In this example, the local preference value is set to 200.

Step 13

end

Example:

Router(config-route-map)# end

Exits route map configuration mode and enters privileged EXEC mode.

Step 14

show ip bgp neighbors [neighbor-address]

Example:

Router(config-router-af)# show ip bgp neighbors 192.168.1.2

(Optional) Displays information about the TCP and BGP connections to neighbors.

Examples

The following partial output from the show ip bgp neighbors command shows information about the TCP and BGP connections to the BGP neighbor 192.168.2.1. This peer supports route refresh.

BGP neighbor is 192.168.1.2, remote AS 40000, external link

Neighbor capabilities:

Route refresh: advertised and received(new)

The following partial output from the show ip bgp neighbors command shows information about the TCP and BGP connections to the BGP neighbor 192.168.3.2. This peer does not support route refresh so the soft-reconfig inbound paths for BGP peer 192.168.3.2 will be stored because there is no other way to update any inbound policy updates.

BGP neighbor is 192.168.3.2, remote AS 50000, external link

Neighbor capabilities:

Route refresh: advertised

The following sample output from the show ip bgp command shows the entry for the network 172.17.1.0. Both BGP peers are advertising 172.17.1.0/24 but only the received-only path is stored for 192.168.3.2.

DETAILED STEPS

This command is used to clear and reset BGP neighbor sessions. Specific neighbors or peer groups can be cleared by using the ip-address and peer-group-name arguments. If no argument is specified, this command will clear and reset all BGP neighbor sessions.

Note The clear ip bgp * command also clears all the internal BGP structures which makes it useful as a troubleshooting tool.

The following example clears and resets all the BGP neighbor sessions. In Cisco IOS Release 12.2(25)S and later releases, the syntax is clear ip bgpall.

This command is used to display all the BGP paths in the database. The following example displays BGP path information for Router B in Figure 3:

Router# show ip bgp paths

Address Hash Refcount Metric Path

0x2FB5DB0 0 5 0 i

0x2FB5C90 1 4 0 i

0x2FB5C00 1361 2 0 50000 i

0x2FB5D20 2625 2 0 40000 i

Step 6 show ip bgp summary

This command is used to display the status of all BGP connections. The following example displays BGP routing table information for Router B in Figure 3:

Router# show ip bgp summary

BGP router identifier 172.17.1.99, local AS number 45000

BGP table version is 3, main routing table version 3

2 network entries using 234 bytes of memory

2 path entries using 104 bytes of memory

4/2 BGP path/bestpath attribute entries using 496 bytes of memory

2 BGP AS-PATH entries using 48 bytes of memory

0 BGP route-map cache entries using 0 bytes of memory

0 BGP filter-list cache entries using 0 bytes of memory

BGP using 882 total bytes of memory

BGP activity 14/10 prefixes, 16/12 paths, scan interval 60 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

192.168.1.2 4 40000 667 672 3 0 0 00:03:49 1

192.168.3.2 4 50000 468 467 0 0 0 00:03:49 (NoNeg)

Aggregating Route Prefixes Using BGP

BGP peers exchange information about local networks but this can quickly lead to large BGP routing tables. CIDR enables the creation of aggregate routes (or supernets) to minimize the size of routing tables. Smaller BGP routing tables can reduce the convergence time of the network and improve network performance. Aggregated routes can be configured and advertised using BGP. Some aggregations advertise only summary routes and other methods of aggregating routes allow more specific routes to be forwarded. Aggregation applies only to routes that exist in the BGP routing table. An aggregated route is forwarded if at least one more specific route of the aggregation exists in the BGP routing table. Perform one of the following tasks to aggregate routes within BGP:

Redistributing a Static Aggregate Route Into BGP

Use this task to redistribute a static aggregate route into BPG. A static aggregate route is configured and then redistributed into the BGP routing table. The static route must be configured to point to interface null 0 and the prefix should be a superset of known BGP routes. When a router receives a BGP packet it will use the more specific BGP routes. If the route is not found in the BGP routing table, then the packet will be forwarded to null 0 and discarded.

Configuring Conditional Aggregate Routes Using BGP

Use this task to create an aggregate route entry in the BGP routing table when at least one specific route falls into the specified range. The aggregate route is advertised as originating from your autonomous system.

AS-SET Generation

AS-SET information can be generated when BGP routes are aggregated using the aggregate-address command. The path advertised for such a route is an AS-SET consisting of all the elements, including the communities, contained in all the paths that are being summarized. If the AS-PATHs to be aggregated are identical, only the AS-PATH is advertised. The ATOMIC-AGGREGATE attribute, set by default for the aggregate-address command, is not added to the AS-SET.

SUMMARY STEPS

1. enable

2. configureterminal

3. router bgp autonomous-system-number

4. aggregate-addressaddressmask [as-set]

5. exit

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Router> enable

Enables privileged EXEC mode.

•Enter your password if prompted.

Step 2

configureterminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3

router bgp autonomous-system-number

Example:

Router(config)# router bgp 45000

Enters router configuration mode for the specified routing process.

Step 4

aggregate-address address mask [as-set]

Example:

Router(config-router)# aggregate-address 172.0.0.0 255.0.0.0 as-set

Creates an aggregate entry in a BGP routing table.

•A specified route must exist in the BGP table.

•Use the aggregate-address command with no keywords to create an aggregate entry if any more-specific BGP routes are available that fall in the specified range.

•Use the as-set keyword to specify that the path advertised for this route is an AS-SET. Do not use the as-set keyword when aggregating many paths because this route is withdrawn and updated every time the reachability information for the aggregated route changes.

Suppressing and Unsuppressing Advertising Aggregated Routes Using BGP

Use this task to create an aggregate route, suppress the advertisement of routes using BGP, and subsequently unsuppress the advertisement of routes. Routes that are suppressed are not advertised to any neighbors, but it is possible to unsuppress routes that were previously suppressed to specific neighbors.

•Use the optional summary-only keyword to create the aggregate route (for example, 10.*.*.*) and also suppresses advertisements of more-specific routes to all neighbors.

•Use the optional suppress-map keyword to create the aggregate route but suppress advertisement of specified routes. Routes that are suppressed are not advertised to any neighbors. You can use the match clauses of route maps to selectively suppress some more-specific routes of the aggregate and leave others unsuppressed. IP access lists and autonomous system path access lists match clauses are supported.

•In this example, the routes previously suppressed in Step 5 are advertised to neighbor 192.168.1.2.

Step 7

exit

Example:

Router(config-router)# exit

Exits router configuration mode and enters global configuration mode.

Suppressing Inactive Route Advertisement Using BGP

Perform this task to suppress the advertisement of inactive routes by BGP. In Cisco IOS Release 12.2(25)S and 12.2(33)SXH, the bgp suppress-inactive command was introduced to configure BGP to not advertise inactive routes to any BGP peer. A BGP routing process can advertise routes that are not installed in the RIB to BGP peers by default. A route that is not installed into the RIB is an inactive route. Inactive route advertisement can occur, for example, when routes are advertised through common route aggregation.

Inactive route advertisements can be suppressed to provide more consistent data forwarding. This feature can be configured on a per IPv4 address family basis. For example, when specifying the maximum number of routes that can be configured in a VRF with the maximum routes global configuration command, you also suppress inactive route advertisement to prevent inactive routes from being accepted into the VRF after route limit has been exceeded.

Prerequisites

This task assumes that BGP is enabled and peering has been established.

Restrictions

Inactive route suppression can be configured only under the IPv4 address family or under a default IPv4 general session.

Examples

The following example shows output from the show ip bgp rib-failure command displaying routes that are not installed in the RIB. The output shows that the displayed routes were not installed because a route or routes with a better administrative distance already exist in the RIB.

Router# show ip bgp rib-failure

Network Next Hop RIB-failure RIB-NH Matches

10.1.15.0/24 10.1.35.5 Higher admin distance n/a

10.1.16.0/24 10.1.15.1 Higher admin distance n/a

Conditionally Advertising BGP Routes

Perform this task to conditionally advertise selected BGP routes. The routes or prefixes that will be conditionally advertised are defined in two route maps, an advertise map and an exist map or nonexist map. The route map associated with the exist map or nonexist map specifies the prefix that the BGP speaker will track. The route map associated with the advertise map specifies the prefix that will be advertised to the specified neighbor when the condition is met. When an exist map is configured, the condition is met when the prefix exists in both the advertise map and the exist map. When a nonexist map is configured, the condition is met when the prefix exists in the advertise map but does not exist in the nonexist map. If the condition is not met, the route is withdrawn and conditional advertisement does not occur. All routes that may be dynamically advertised or not advertised need to exist in the BGP routing table for conditional advertisement to occur. These routes are referenced from an access list or an IP prefix list.

•In this example, access list 1 permits advertising of the 172.17.0.0. prefix depending on other conditions set by the neighbor advertise-map command.

Step 12

Repeat Step 11 for every access list to be created.

—

Step 13

exit

Example:

Router(config)# exit

Exits global configuration mode and returns to privileged EXEC mode.

Step 14

exit

Example:

Router(config-router)# exit

Exits router configuration mode and enters global configuration mode.

Originating BGP Routes

Route aggregation is useful to minimize the size of the BGP table but there are situations when you want to add more specific prefixes to the BGP table. Route aggregation can hide more specific routes. Using the network command as shown in "Configuring a BGP Routing Process" section originates routes and the following optional tasks originate BGP routes for the BGP table for different situations.

Advertising a Default Route Using BGP

Perform this task to advertise a default route to BGP peers. The default route is locally originated. A default route can be useful to simplify configuration or to prevent the router from using too many system resources. If the router is peered with an Internet service provider (ISP), the ISP will carry full routing tables, so configuring a default route into the ISP network saves resources at the local router.

(Optional) Permits a BGP speaker—the local router—to send the default route 0.0.0.0 to a peer for use as a default route.

Step 9

exit

Example:

Router(config-router)# exit

Exits router configuration mode and enters global configuration mode.

Troubleshooting Tips

Use the show ip route command on the receiving BGP peer (not on the local router) to verify that the default route has been set. In the output, verify that a line similar to the following showing the default route 0.0.0.0 is present:

B* 0.0.0.0/0 [20/0] via 192.168.1.2, 00:03:10

Conditionally Injecting BGP Routes

Use this task to inject more specific prefixes into a BGP routing table over less specific prefixes that were selected through normal route aggregation. These more specific prefixes can be used to provide a finer granularity of traffic engineering or administrative control than is possible with aggregated routes.

Conditional BGP Route Injection

Routes that are advertised through the BGP are commonly aggregated to minimize the number of routes that are used and reduce the size of global routing tables. However, common route aggregation can obscure more specific routing information that is more accurate but not necessary to forward packets to their destinations. Routing accuracy is obscured by common route aggregation because a prefix that represents multiple addresses or hosts over a large topological area cannot be accurately reflected in a single route. Cisco IOS software provides several methods in which you can originate a prefix into BGP. The existing methods include redistribution and using the network or aggregate-address command. These methods assume the existence of more specific routing information (matching the route to be originated) in either the routing table or the BGP table.

BGP conditional route injection allows you to originate a prefix into a BGP routing table without the corresponding match. This feature allows more specific routes to be generated based on administrative policy or traffic engineering information in order to provide more specific control over the forwarding of packets to these more specific routes, which are injected into the BGP routing table only if the configured conditions are met. Enabling this feature will allow you to improve the accuracy of common route aggregation by conditionally injecting or replacing less specific prefixes with more specific prefixes. Only prefixes that are equal to or more specific than the original prefix may be injected. BGP conditional route injection is enabled with the bgp inject-map exist-map command and uses two route maps (inject map and exist map) to install one (or more) more specific prefixes into a BGP routing table. The exist-map specifies the prefixes that the BGP speaker will track. The inject map defines the prefixes that will be created and installed into the local BGP table.

Prerequisites

This task assumes that the IGP is already configured for the BGP peers.

•In this example, the prefix list named SOURCE is configured to permit routes from network 10.1.1.0/24.

Step 15

Repeat Step 14 for every prefix list to be created.

—

Step 16

exit

Example:

Router(config)# exit

Exits global configuration mode and returns to privileged EXEC mode.

Step 17

show ip bgp injected-paths

Example:

Router# show ip bgp injected-paths

(Optional) Displays information about injected paths.

Examples

The following sample output is similar to the output that will be displayed when the show ip bgp injected-paths command is entered:

Router# show ip bgp injected-paths

BGP table version is 11, local router ID is 10.0.0.1

Status codes:s suppressed, d damped, h history, * valid, > best, i -

internal

Origin codes:i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf Weight Path

*> 172.16.0.0 10.0.0.2 0 ?

*> 172.17.0.0/16 10.0.0.2 0 ?

Troubleshooting Tips

BGP conditional route injection is based on the injection of a more specific prefix into the BGP routing table when a less specific prefix is present. If conditional route injection is not working properly, verify the following:

•If conditional route injection is configured but does not occur, verify the existence of the aggregate prefix in the BGP routing table. The existence (or not) of the tracked prefix in the BGP routing table can be verified with the show ip bgp command.

•If the aggregate prefix exists but conditional route injection does not occur, verify that the aggregate prefix is being received from the correct neighbor and the prefix list identifying that neighbor is a /32 match.

•Verify the injection (or not) of the more specific prefix using the show ip bgp injected-paths command.

•Verify that the prefix that is being injected is not outside of the scope of the aggregate prefix.

Ensure that the inject route map is configured with the set ip address command and not the match ip address command.

Originating BGP Routes Using Backdoor Routes

Use this task to indicate to border routers which networks are reachable using a backdoor route. A backdoor network is treated the same as a local network except that it is not advertised.

BGP Backdoor Routes

In a BGP network topology with two border routers using eBGP to communicate to a number of different autonomous systems, using eBGP to communicate between the two border routers may not be the most efficient routing method. In Figure 4 Router C as a BGP speaker will receive a route to Router D through eBGP but this route will traverse a number of other autonomous systems. Router C and Router D are also connected through an Enhanced Interior Gateway Routing Protocol (EIGRP) network (any IGP can be used here) and this route has a shorter path. EIGRP routes, however, have a default administrative distance of 90 and eBGP routes have a default administrative distance of 20 so BGP will prefer the eBGP route. Changing the default administrative distances is not recommended because changing the administrative distance may lead to routing loops. To cause BGP to prefer the EIGRP route you can use the network backdoor command. BGP treats the network specified by the network backdoor command as a locally assigned network, except that it does not advertise the specified network in BGP updates. In Figure 4 this means that Router C will communicate to Router D using the shorter EIGRP route instead of the longer eBGP route.

Figure 4 BGP Backdoor Route Topology

Prerequisites

This task assumes that the IGP—EIGRP in this example—is already configured for the BGP peers. The configuration is done at Router C in Figure 4 and the BGP peer is Router D.

SUMMARY STEPS

1. enable

2. configureterminal

3. router bgp autonomous-system-number

4. neighbor ip-address remote-as autonomous-system-number

5. network ip-address backdoor

6. end

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Router> enable

Enables privileged EXEC mode.

•Enter your password if prompted.

Step 2

configureterminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3

router bgp autonomous-system-number

Example:

Router(config)# router bgp 45000

Enters router configuration mode for the specified routing process.

Step 4

neighbor ip-address remote-as autonomous-system-number

Example:

Router(config-router)# neighbor 172.22.1.2 remote-as 45000

Adds the IP address of the neighbor in the specified autonomous system to the multiprotocol BGP neighbor table of the local router.

Step 5

network ip-address backdoor

Example:

Router(config-router)# network 172.21.1.0 backdoor

Indicates a network that is reachable through a backdoor route.

Step 6

end

Example:

Router(config-router)# end

Exits router configuration mode and returns to privileged EXEC mode.

Configuring a BGP Peer Group

This task explains how to configure a BGP peer group. Often, in a BGP speaker, many neighbors are configured with the same update policies (that is, the same outbound route maps, distribute lists, filter lists, update source, and so on). Neighbors with the same update policies can be grouped into peer groups to simplify configuration and, more importantly, to make updating more efficient. When you have many peers, this approach is highly recommended.

The three steps to configure a BGP peer group, described in the following task, are as follows:

•Creating the peer group

•Assigning options to the peer group

•Making neighbors members of the peer group

You can disable a BGP peer or peer group without removing all the configuration information using the neighbor shutdown router configuration command.

Restrictions

By default, neighbors that are defined using the neighbor remote-as command in router configuration mode exchange only IPv4 unicast address prefixes. To exchange other address prefix types, such as IPv6 prefixes, neighbors must also be activated using the neighbor activate command in address family configuration mode for the other prefix types.

SUMMARY STEPS

1. enable

2. configureterminal

3. router bgp autonomous-system-number

4. neighbor peer-group-name peer-group

5. neighbor ip-address remote-as autonomous-system-number

6. neighbor ip-address peer-group peer-group-name

7. address-family ipv4 [unicast | multicast| vrf vrf-name]

8. neighbor peer-group-name activate

9. neighbor ip-address peer-group peer-group-name

10. end

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Router> enable

Enables privileged EXEC mode.

•Enter your password if prompted.

Step 2

configureterminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3

router bgp autonomous-system-number

Example:

Router(config)# router bgp 40000

Enters router configuration mode for the specified routing process.

Step 4

neighbor peer-group-name peer-group

Example:

Router(config-router)# neighbor fingroup peer-group

Creates a BGP peer group.

Step 5

neighbor ip-address remote-as autonomous-system-number

Example:

Router(config-router)# neighbor 192.168.1.1 remote-as 45000

Adds the IP address of the neighbor in the specified autonomous system to the multiprotocol BGP neighbor table of the local router.

Step 6

neighbor ip-address peer-group peer-group-name

Example:

Router(config-router)# neighbor 192.168.1.1 peer-group fingroup

Assigns the IP address of a BGP neighbor to a peer group.

Step 7

address-family ipv4 [unicast | multicast | vrf vrf-name]

Example:

Router(config-router)# address-family ipv4 multicast

Specifies the IPv4 address family and enters address family configuration mode.

•The unicast keyword specifies the IPv4 unicast address family. This is the default.

Enables the neighbor to exchange prefixes for the IPv4 address family with the local router.

Note By default, neighbors that are defined using the neighbor remote-as command in router configuration mode exchange only unicast address prefixes. To allow BGP to exchange other address prefix types, such as multicast that is configured in this example, neighbors must also be activated using the neighbor activate command.

Inheritance in Peer Templates

The inheritance capability is a key component of peer template operation. Inheritance in a peer template is similar to node and tree structures commonly found in general computing, for example, file and directory trees. A peer template can directly or indirectly inherit the configuration from another peer template. The directly inherited peer template represents the tree in the structure. The indirectly inherited peer template represents a node in the tree. Because each node also supports inheritance, branches can be created that apply the configurations of all indirectly inherited peer templates within a chain back to the directly inherited peer template or the source of the tree. This structure eliminates the need to repeat configuration statements that are commonly reapplied to groups of neighbors because common configuration statements can be applied once and then indirectly inherited by peer templates that are applied to neighbor groups with common configurations. Configuration statements that are duplicated separately within a node and a tree are filtered out at the source of the tree by the directly inherited template. A directly inherited template will overwrite any indirectly inherited statements that are duplicated in the directly inherited template.

Inheritance expands the scalability and flexibility of neighbor configuration by allowing you to chain together peer templates configurations to create simple configurations that inherit common configuration statements or complex configurations that apply very specific configuration statements along with common inherited configurations. Specific details about configuring inheritance in peer session templates and peer policy templates are provided in the following sections.

When BGP neighbors use inherited peer templates it can be difficult to determine which policies are associated with a specific template. In Cisco IOS 12.0(25)S, 12.4(11)T and later releases the detail keyword was added to the show ip bgp template peer-policy command to display the detailed configuration of local and inherited policies associated with a specific template.

Configuring a Basic Peer Session Template

Perform this task to create a basic peer session template with general BGP routing session commands that can be applied to many neighbors using one of the next two tasks.

Note The commands in Step 5 and 6 are optional and could be replaced with any supported general session commands.

Peer Session Templates

Peer session templates are used to group and apply the configuration of general session commands to groups of neighbors that share session configuration elements. General session commands that are common for neighbors that are configured in different address families can be configured within the same peer session template. Peer session templates are created and configured in peer session configuration mode. Only general session commands can be configured in a peer session template. The following general session commands are supported by peer session templates:

•description

•disable-connected-check

•ebgp-multihop

•exit peer-session

•inherit peer-session

•local-as

•password

•remote-as

•shutdown

•timers

•translate-update

•update-source

•version

General session commands can be configured once in a peer session template and then applied to many neighbors through the direct application of a peer session template or through indirect inheritance from a peer session template. The configuration of peer session templates simplifies the configuration of general session commands that are commonly applied to all neighbors within an autonomous system.

Peer session templates support direct and indirect inheritance. A peer can be configured with only one peer session template at a time, and that peer session template can contain only one indirectly inherited peer session template.

Note If you attempt to configure more than one inherit statement with a single peer session template, an error message will be displayed.

This behavior allows a BGP neighbor to directly inherit only one session template and indirectly inherit up to seven additional peer session templates. This allows you to apply up to a maximum of eight peer session configurations to a neighbor: the configuration from the directly inherited peer session template and the configurations from up to seven indirectly inherited peer session templates. Inherited peer session configurations are evaluated first and applied starting with the last node in the branch and ending with the directly applied peer session template configuration at the of the source of the tree. The directly applied peer session template will have priority over inherited peer session template configurations. Any configuration statements that are duplicated in inherited peer session templates will be overwritten by the directly applied peer session template. So, if a general session command is reapplied with a different value, the subsequent value will have priority and overwrite the previous value that was configured in the indirectly inherited template. The following examples illustrate the use of this feature.

In the following example, the general session command remote-as 1 is applied in the peer session template named SESSION-TEMPLATE-ONE:

template peer-session SESSION-TEMPLATE-ONE

remote-as 1

exit peer-session

Peer session templates support only general session commands. BGP policy configuration commands that are configured only for a specific address family or NLRI configuration mode are configured with peer policy templates.

Restrictions

The following restrictions apply to the peer session templates:

•A peer session template can directly inherit only one session template, and each inherited session template can also contain one indirectly inherited session template. So, a neighbor or neighbor group can be configured with only one directly applied peer session template and seven additional indirectly inherited peer session templates.

•A BGP neighbor cannot be configured to work with both peer groups and peer templates. A BGP neighbor can be configured to belong only to a peer group or to inherit policies only from peer templates.

•The output can be filtered to display a single peer policy template with the session-template-name argument. This command also supports all standard output modifiers.

What to Do Next

After the peer session template is created, the configuration of the peer session template can be inherited or applied by another peer session template with the inherit peer-session or neighbor inherit peer-session command.

This task configures peer session template inheritance with the inherit peer-session command. It creates and configures a peer session template and allows it to inherit a configuration from another peer session template.

Note The commands in Steps 5 and 6 are optional and could be replaced with any supported general session commands.

Configures this peer session template to inherit the configuration of another peer session template.

•The example configures this peer session template to inherit the configuration from INTERNAL-BGP. This template can be applied to a neighbor, and the configuration INTERNAL-BGP will be applied indirectly. No additional peer session templates can be directly applied. However, the directly inherited template can contain up to seven indirectly inherited peer session templates.

•The output can be filtered to display a single peer policy template with the optional session-template-name argument. This command also supports all standard output modifiers.

What to Do Next

After the peer session template is created, the configuration of the peer session template can be inherited or applied by another peer session template with the inherit peer-session or neighbor inherit peer-session command.

This task configures a router to send a peer session template to a neighbor to inherit the configuration from the specified peer session template with the neighbor inherit peer-session command. Use the following steps to send a peer session template configuration to a neighbor to inherit:

SUMMARY STEPS

1. enable

2. configure terminal

3. router bgp autonomous-system-number

4. neighborip-addressremote-asautonomous-system-number

5. neighborip-addressinherit peer-sessionsession-template-name

6. exit

7. show ip bgp template peer-session [session-template-name]

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Router> enable

Enables privileged EXEC mode.

•Enter your password if prompted.

Step 2

configureterminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3

router bgp autonomous-system-number

Example:

Router(config)# router bgp 101

Enters router configuration mode and creates a BGP routing process.

Step 4

neighborip-addressremote-as autonomous-system-number

Example:

Router(config-router)# neighbor 172.16.0.1 remote-as 202

Configures a peering session with the specified neighbor.

•The explicit remote-as statement is required for the neighbor inherit statement in Step 5 to work. If a peering is not configured, the specified neighbor in Step 5 will not accept the session template.

Step 5

neighborip-addressinherit peer-sessionsession-template-name

Example:

Router(config-router)# neighbor 172.16.0.1 inherit peer-session CORE1

Sends a peer session template to a neighbor so that the neighbor can inherit the configuration.

•The example configures a router to send the peer session template named CORE1 to the 172.16.0.1 neighbor to inherit. This template can be applied to a neighbor, and if another peer session template is indirectly inherited in CORE1, the indirectly inherited configuration will also be applied. No additional peer session templates can be directly applied. However, the directly inherited template can also inherit up to seven additional indirectly inherited peer session templates.

Step 6

end

Example:

Router(config-router)# exit

Exits router configuration mode and enters privileged EXEC mode.

Step 7

show ip bgp template peer-session [session-template-name]

Example:

Router#> show ip bgp template peer-session

Displays locally configured peer session templates.

•The output can be filtered to display a single peer policy template with the optional session-template-name argument. This command also supports all standard output modifiers.

Configuring Basic Peer Policy Templates

Perform this task to create a basic peer policy template with BGP policy configuration commands that can be applied to many neighbors using one of the next two tasks.

Note The commands in Steps 5 through 7 are optional and could be replaced with any supported BGP policy configuration commands.

Peer Policy Templates

Peer policy templates are used to group and apply the configuration of commands that are applied within specific address families and NLRI configuration mode. Peer policy templates are created and configured in peer policy configuration mode. BGP policy commands that are configured for specific address families are configured in a peer policy template. The following BGP policy commands are supported by peer policy templates:

•advertisement-interval

•allowas-in

•as-override

•capability

•default-originate

•distribute-list

•dmzlink-bw

•exit-peer-policy

•filter-list

•inherit peer-policy

•maximum-prefix

•next-hop-self

•next-hop-unchanged

•prefix-list

•remove-private-as

•route-map

•route-reflector-client

•send-community

•send-label

•soft-reconfiguration

•unsuppress-map

•weight

Peer policy templates are used to configure BGP policy commands that are configured for neighbors that belong to specific address families. Like peer session templates, peer policy templates are configured once and then applied to many neighbors through the direct application of a peer policy template or through inheritance from peer policy templates. The configuration of peer policy templates simplifies the configuration of BGP policy commands that are applied to all neighbors within an autonomous system.

Like peer session templates, a peer policy template supports inheritance. However, there are minor differences. A directly applied peer policy template can directly or indirectly inherit configurations from up to seven peer policy templates. So, a total of eight peer policy templates can be applied to a neighbor or neighbor group. Inherited peer policy templates are configured with sequence numbers like route maps. An inherited peer policy template, like a route map, is evaluated starting with the inherit statement with the lowest sequence number and ending with the highest sequence number. However, there is a difference; a peer policy template will not collapse like a route map. Every sequence is evaluated, and if a BGP policy command is reapplied with a different value, it will overwrite any previous value from a lower sequence number.

The directly applied peer policy template and the inherit statement with the highest sequence number will always have priority and be applied last. Commands that are reapplied in subsequent peer templates will always overwrite the previous values. This behavior is designed to allow you to apply common policy configurations to large neighbor groups and specific policy configurations only to certain neighbors and neighbor groups without duplicating individual policy configuration commands.

Peer policy templates support only policy configuration commands. BGP policy configuration commands that are configured only for specific address families are configured with peer policy templates.

The configuration of peer policy templates simplifies and improves the flexibility of BGP configuration. A specific policy can be configured once and referenced many times. Because a peer policy supports up to eight levels of inheritance, very specific and very complex BGP policies can also be created.

This task configures peer policy template inheritance using the inherit peer-policy command. It creates and configure a peer policy template and allows it to inherit a configuration from another peer policy template.

When BGP neighbors use inherited peer templates, it can be difficult to determine which policies are associated with a specific template. In Cisco IOS Release 12.0(25)S, 12.4(11)T, 12.2(33)SRB, and later releases, the detail keyword was added to the show ip bgp template peer-policy command to display the detailed configuration of local and inherited policies associated with a specific template.

Note The commands in Steps 5 and 6 are optional and could be replaced with any supported BGP policy configuration commands.

Configures the peer policy template to inherit the configuration of another peer policy template.

•The sequence-number argument sets the order in which the peer policy template is evaluated. Like a route map sequence number, the lowest sequence number is evaluated first.

•The example configures this peer policy template to inherit the configuration from GLOBAL. If the template created in these steps is applied to a neighbor, the configuration GLOBAL will also be inherited and applied indirectly. Up to six additional peer policy templates can be indirectly inherited from GLOBAL for a total of eight directly applied and indirectly inherited peer policy templates.

•This template in the example will be evaluated first if no other templates are configured with a lower sequence number.

•The output can be filtered to display a single peer policy template with the policy-template-name argument. This command also supports all standard output modifiers.

•Use the detail keyword to display detailed policy information.

Note The detail keyword is supported only in Cisco IOS Release 12.0(25)S, 12.4(11)T, 12.2(33)SRB, and later releases.

Examples

The following sample output of the show ip bgp template peer-policy command with the detail keyword displays details of the policy named NETWORK1. The output in this example shows that the GLOBAL template was inherited. Details of route map and prefix list configurations are also displayed.

This task configures a router to send a peer policy template to a neighbor to inherit using the neighbor inherit peer-policy command. Perform the following steps to send a peer policy template configuration to a neighbor to inherit.

When BGP neighbors use multiple levels of peer templates it can be difficult to determine which policies are applied to the neighbor. In Cisco IOS Release 12.0(25)S, 12.4(11)T, 12.2(33)SRB, and later releases, the policy and detail keywords were added to the show ip bgp neighbors command to display the inherited policies and policies configured directly on the specified neighbor.

SUMMARY STEPS

1. enable

2. configure terminal

3. router bgp autonomous-system-number

4. neighborip-addressremote-asautonomous-system-number

5. address-family ipv4[multicast| unicast| vrfvrf-name]

6. neighborip-addressinherit peer-policypolicy-template-name

7. end

8. show ip bgp neighbors [ip-address [policy[detail]]]

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Router> enable

Enables privileged EXEC mode.

•Enter your password if prompted.

Step 2

configureterminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3

router bgp autonomous-system-number

Example:

Router(config)# router bgp 45000

Enters router configuration mode and creates a BGP routing process.

Step 4

neighbor ip-addressremote-asautonomous-system-number

Example:

Router(config-router)# neighbor 192.168.1.2 remote-as 40000

Configures a peering session with the specified neighbor.

•The explicit remote-as statement is required for the neighbor inherit statement in Step 5 to work. If a peering is not configured, the specified neighbor in Step 5 will not accept the session template.

Sends a peer policy template to a neighbor so that the neighbor can inherit the configuration.

•The example configures a router to send the peer policy template named GLOBAL to the 192.168.1.2 neighbor to inherit. This template can be applied to a neighbor, and if another peer policy template is indirectly inherited from GLOBAL, the indirectly inherited configuration will also be applied. Up to seven additional peer policy templates can be indirectly inherited from GLOBAL.

Examples

The following sample output shows the policies applied to the neighbor at 192.168.1.2. The output displays both inherited policies and policies configured on the neighbor device. Inherited polices are policies that the neighbor inherits from a peer-group or a peer-policy template.

Router# show ip bgp neighbors 192.168.1.2 policy

Neighbor: 192.168.1.2, Address-Family: IPv4 Unicast

Locally configured policies:

route-map ROUTE in

Inherited polices:

prefix-list NO-MARKETING in

route-map ROUTE in

weight 300

maximum-prefix 10000

Monitoring and Maintaining BGP Dynamic Update Groups

Use this task to clear and display information about the processing of dynamic BGP update groups. The performance of BGP update message generation is improved with the use of BGP update groups. With the configuration of the BGP peer templates and the support of the dynamic BGP update groups, the network operator no longer needs to configure peer groups in BGP and can benefit from improved configuration flexibility and system performance. For more information about using BGP peer templates, see the "Configuring Peer Session Templates" section and the "Configuring Peer Policy Templates" section.

BGP Dynamic Update Group Configuration

In Cisco IOS Release 12.0(24)S, 12.2(18)S, 12.3(4)T, and 12.2(27)SBC and later releases, a new algorithm was introduced that dynamically calculates and optimizes update groups of neighbors that share the same outbound policies and can share the same update messages. No configuration is required to enable the BGP dynamic update group and the algorithm runs automatically. When a change to outbound policy occurs, the router automatically recalculates update group memberships and applies the changes by triggering an outbound soft reset after a 1-minute timer expires. This behavior is designed to provide the network operator with time to change the configuration if a mistake is made. You can manually enable an outbound soft reset before the timer expires by entering the clear ip bgpip-address soft out command.

Note In Cisco IOS Release 12.0(25)S, 12.3(2)T, and prior releases the update group recalculation delay timer is set to 3 minutes.

For the best optimization of BGP update group generation, we recommend that the network operator keeps outbound routing policy the same for neighbors that have similar outbound policies.

SUMMARY STEPS

1. enable

2. clear ip bgp update-group [index-group|ip-address]

3. show ip bgp replication [index-group|ip-address]

4. show ip bgp update-group [index-group|ip-address] [summary]

DETAILED STEPS

Step 1 enable

Enables privileged EXEC mode. Enter your password if prompted.

Router> enable

Step 2 clear ip bgp update-group[index-group | ip-address]

This command is used to clear BGP update membership and recalculate BGP update groups. Specific update groups can be cleared by using the index-group argument. The range of update group index numbers is from 1 to 4294967295. Specific neighbors can be cleared by using the ip-address argument. If no argument is specified, this command will clear and recalculate all BGP update groups.

The following example clears the membership of neighbor 192.168.2.2 from an update group:

Router# clear ip bgp update-group 192.168.2.2

Step 3 show ip bgp replication[index-group | ip-address]

This command displays BGP update group replication statistics. Specific update group replication statistics can be displayed by using the index-group argument. The range of update group index numbers is from 1 to 4294967295. Specific update group replication statistics can be displayed by using the ip-address argument. If no argument is specified, this command will display replication statistics for all update groups.

The following example displays update group replication information for all BGP neighbors:

Router# show ip bgp replication

BGP Total Messages Formatted/Enqueued : 0/0

Index Type Members Leader MsgFmt MsgRepl Csize Qsize

1 internal 1 192.168.1.2 0 0 0 0

2 internal 2 192.168.3.2 0 0 0 0

Step 4 show ip bgp update-group[index-group | ip-address] [summary]

This command is used to display information about BGP update groups. Information about specific update group statistics can be displayed by using the index-group argument. The range of update group index numbers is from 1 to 4294967295. Information about specific update groups can be displayed by using the ip-address argument. If no argument is specified, this command will display statistics for all update groups. Summary information can be displayed by using the summary keyword.

The following example displays update group information for all neighbors:

Router# show ip bgp update-group

BGP version 4 update-group 1, external, Address Family: IPv4 Unicast

BGP Update version : 8/0, messages 0

Update messages formatted 11, replicated 3

Number of NLRIs in the update sent: max 1, min 0

Minimum time between advertisement runs is 30 seconds

Has 2 members (* indicates the members currently being sent updates):

192.168.1.2 192.168.3.2

Troubleshooting Tips

Use the debug ip bgp groups command to display information about the processing of BGP update groups. Information can be displayed for all update groups, an individual update group, or a specific BGP neighbor. The output of this command can be very verbose. This command should not be deployed in a production network unless your are troubleshooting a problem.

Configuring a BGP Process and Customizing Peers: Example

The following example shows the configuration for Router B in Figure 3 with a BGP process configured with two neighbor peers (at Router A and at Router E) in separate autonomous systems. IPv4 unicast routes are exchanged with both peers and IPv4 multicast routes are exchanged with the BGP peer at Router E.

Router B

router bgp 45000

bgp router-id 172.17.1.99

no bgp default ipv4-unicast

bgp log-neighbor-changes

timers bgp 70 120

neighbor 192.168.1.2 remote-as 40000

neighbor 192.168.3.2 remote-as 50000

neighbor 192.168.3.2 description finance

!

address-family ipv4

neighbor 192.168.1.2 activate

neighbor 192.168.3.2 activate

no auto-summary

no synchronization

network 172.17.1.0 mask 255.255.255.0

exit-address-family

!

address-family ipv4 multicast

neighbor 192.168.3.2 activate

neighbor 192.168.3.2 advertisement-interval 25

no auto-summary

no synchronization

network 172.17.1.0 mask 255.255.255.0

exit-address-family

NLRI to AFI Configuration: Example

The following example upgrades an existing router configuration file in the NLRI format to the AFI format and set the router CLI to use only commands in the AFI format:

router bgp 60000

bgp upgrade-cli

The show running-config command can be used in privileged EXEC mode to verify that an existing router configuration file has been upgraded from the NLRI format to the AFI format. The following sections provide sample output from a router configuration file in the NLRI format, and the same router configuration file after it has been upgraded to the AFI format with the bgp upgrade-cli command in router configuration mode.

Note After a router has been upgraded from the AFI format to the NLRI format with the bgp upgrade-cli command, NLRI commands will no longer be accessible or configurable.

Router Configuration File in NLRI Format Prior to Upgrading

The following sample output is from the show running-config command in privileged EXEC mode. The sample output shows a router configuration file, in the NLRI format, prior to upgrading to the AFI format with the bgp upgrade-cli command. The sample output is filtered to show only the affected portion of the router configuration.

Router# show running-config | begin bgp

router bgp 101

no synchronization

bgp log-neighbor-changes

neighbor 10.1.1.1 remote-as 505 nlri unicast multicast

no auto-summary

!

ip default-gateway 10.4.9.1

ip classless

!

!

route-map REDISTRIBUTE-MULTICAST permit 10

match ip address prefix-list MULTICAST-PREFIXES

set nlri multicast

!

route-map MULTICAST-PREFIXES permit 10

!

route-map REDISTRIBUTE-UNICAST permit 20

match ip address prefix-list UNICAST-PREFIXES

set nlri unicast

!

!

!

line con 0

line aux 0

line vty 0 4

password PASSWORD

login

!

end

Router Configuration File in AFI Format After Upgrading

The following sample output shows the router configuration file after it has been upgraded to the AFI format. The sample output is filtered to show only the affected portion of the router configuration file.

Router# show running-config | begin bgp

router bgp 101

bgp log-neighbor-changes

neighbor 10.1.1.1 remote-as 505

no auto-summary

!

address-family ipv4 multicast

neighbor 10.1.1.1 activate

no auto-summary

no synchronization

exit-address-family

!

address-family ipv4

neighbor 10.1.1.1 activate

no auto-summary

no synchronization

exit-address-family

!

ip default-gateway 10.4.9.1

ip classless

!

!

route-map REDISTRIBUTE-MULTICAST_mcast permit 10

match ip address prefix-list MULTICAST-PREFIXES

!

route-map REDISTRIBUTE-MULTICAST permit 10

match ip address prefix-list MULTICAST-PREFIXES

!

route-map MULTICAST-PREFIXES permit 10

!

route-map REDISTRIBUTE-UNICAST permit 20

match ip address prefix-list UNICAST-PREFIXES

!

!

!

line con 0

line aux 0

line vty 0 4

password PASSWORD

login

!

end

BGP Soft Reset: Examples

The following examples show two ways to reset the connection for BGP peer 192.168.1.1.

Dynamic Inbound Soft Reset Example

The following example shows the clear ip bgp 192.168.1.1 soft in EXEC command used to initiate a dynamic soft reconfiguration in the BGP peer 192.168.1.1. This command requires that the peer support the route refresh capability.

clear ip bgp 192.168.1.1 soft in

Inbound Soft Reset Using Stored Information Example

The following example shows how to enable inbound soft reconfiguration for the neighbor 192.168.1.1. All the updates received from this neighbor will be stored unmodified, regardless of the inbound policy. When inbound soft reconfiguration is performed later, the stored information will be used to generate a new set of inbound updates.

router bgp 100

neighbor 192.168.1.1 remote-as 200

neighbor 192.168.1.1 soft-reconfiguration inbound

The following example clears the session with the neighbor 192.168.1.1:

clear ip bgp 192.168.1.1 soft in

Aggregating Prefixes Using BGP: Examples

The following examples show how you can use aggregate routes in BGP either by redistributing an aggregate route into BGP or by using the BGP conditional aggregation routing feature.

In the following example, the redistribute static router configuration command is used to redistribute aggregate route 10.0.0.0:

ip route 10.0.0.0 255.0.0.0 null 0

!

router bgp 100

redistribute static

The following configuration shows how to create an aggregate entry in the BGP routing table when at least one specific route falls into the specified range. The aggregate route will be advertised as coming from your autonomous system and has the atomic aggregate attribute set to show that information might be missing. (By default, atomic aggregate is set unless you use the as-set keyword in the aggregate-address router configuration command.)

router bgp 100

aggregate-address 10.0.0.0 255.0.0.0

The following example shows how to create an aggregate entry using the same rules as in the previous example, but the path advertised for this route will be an AS-SET consisting of all elements contained in all paths that are being summarized:

router bgp 100

aggregate-address 10.0.0.0 255.0.0.0 as-set

The following example shows how to create the aggregate route for 10.0.0.0 and also suppress advertisements of more specific routes to all neighbors:

router bgp 100

aggregate-address 10.0.0.0 255.0.0.0 summary-only

The following example, starting in global configuration mode, configures BGP to not advertise inactive routes:

Router(config)# router bgp 50000

Router(config-router)# address-family ipv4 unicast

Router(config-router-af)# bgp suppress-inactive

Router(config-router-af)# end

The following example configures a maximum route limit in the VRF named red and configures BGP to not advertise inactive routes through the VRF named RED:

Router(config)# ip vrf RED

Router(config-vrf)# rd 50000:10

Router(config-vrf)# maximum routes 1000 10

Router(config-vrf)# exit

Router(config)# router bgp 50000

Router(config-router)# address-family ipv4 vrf RED

Router(config-router-af)# bgp suppress-inactive

Router(config-router-af)# end

Configuring a BGP Peer Group: Example

The following example shows how to use an address family to configure a peer group so that all members of the peer group are both unicast- and multicast-capable:

router bgp 45000

neighbor 192.168.1.2 remote-as 40000

neighbor 192.168.3.2 remote-as 50000

address-family ipv4 unicast

neighbor mygroup peer-group

neighbor 192.168.1.2 peer-group mygroup

neighbor 192.168.3.2 peer-group mygroup

router bgp 45000

neighbor 192.168.1.2 remote-as 40000

neighbor 192.168.3.2 remote-as 50000

address-family ipv4 multicast

neighbor mygroup peer-group

neighbor 192.168.1.2 peer-group mygroup

neighbor 192.168.3.2 peer-group mygroup

neighbor 192.168.1.2 activate

neighbor 192.168.3.2 activate

Configuring Peer Session Templates: Examples

The following example creates a peer session template named INTERNAL-BGP in session-template configuration mode:

router bgp 45000

template peer-session INTERNAL-BGP

remote-as 50000

timers 30 300

exit-peer-session

The following example creates a peer session template named CORE1. This example inherits the configuration of the peer session template named INTERNAL-BGP.

router bgp 45000

template peer-session CORE1

description CORE-123

update-source loopback 1

inherit peer-session INTERNAL-BGP

exit-peer-session

The following example configures the 192.168.3.2 neighbor to inherit the CORE1 peer session template. The 192.168.3.2 neighbor will also indirectly inherit the configuration from the peer session template named INTERNAL-BGP. The explicit remote-as statement is required for the neighbor inherit statement to work. If a peering is not configured, the specified neighbor will not accept the session template.

router bgp 45000

neighbor 192.168.3.2 remote-as 50000

neighbor 192.168.3.2 inherit peer-session CORE1

Configuring Peer Policy Templates: Examples

The following example creates a peer policy template named GLOBAL in policy-template configuration mode:

router bgp 45000

template peer-policy GLOBAL

weight 1000

maximum-prefix 5000

prefix-list NO_SALES in

exit-peer-policy

The following example creates a peer policy template named PRIMARY-IN in policy-template configuration mode:

template peer-policy PRIMARY-IN

prefix-list ALLOW-PRIMARY-A in

route-map SET-LOCAL in

weight 2345

default-originate

exit-peer-policy

The following example creates a peer policy template named CUSTOMER-A. This peer policy template is configured to inherit the configuration from the peer policy templates named PRIMARY-IN and GLOBAL.

template peer-policy CUSTOMER-A

route-map SET-COMMUNITY in

filter-list 20 in

inherit peer-policy PRIMARY-IN 20

inherit peer-policy GLOBAL 10

exit-peer-policy

The following example configures the 192.168.2.2 neighbor in address family mode to inherit the peer policy template name CUSTOMER-A. The 192.168.2.2 neighbor will also indirectly inherit the peer policy templates named PRIMARY-IN and GLOBAL.

router bgp 45000

neighbor 192.168.2.2 remote-as 50000

address-family ipv4 unicast

neighbor 192.168.2.2 inherit peer-policy CUSTOMER-A

exit

Monitoring and Maintaining BGP Dynamic Update Peer-Groups: Examples

No configuration is required to enable the BGP dynamic update of peer groups and the algorithm runs automatically. The following examples show how BGP update group information can be cleared or displayed.

clear ip bgp update-group Example

The following example clears the membership of neighbor 10.0.0.1 from an update group:

Router#clear ip bgp update-group 10.0.0.1

debug ip bgp groups Example

The following example output from the debug ip bgp groups command shows the recalculation of update groups after the clear ip bgp groups command was issued:

RFCs

Guidelines for Creation, Selection, and Registration of an Autonomous System (AS)

RFC 2519

A Framework for Inter-Domain Route Aggregation

RFC 2858

Multiprotocol Extensions for BGP-4

RFC 2918

Route Refresh Capability for BGP-4

RFC 3392

Capabilities Advertisement with BGP-4

Technical Assistance

Description

Link

The Cisco Technical Support & Documentation website contains thousands of pages of searchable technical content, including links to products, technologies, solutions, technical tips, tools, and technical documentation. Registered Cisco.com users can log in from this page to access even more content.

Feature Information for Configuring a Basic BGP Network

Table 3 lists the features in this module and provides links to specific configuration information. Only features that were introduced or modified in Cisco IOS Releases 12.2(1), 12.0(3)S, 12.2(27)SBC, 12.2(33)SRB, 12.2(33)SXH, or later release appear in the table.

For information on a feature in this technology that is not documented here, see the "Cisco BGP Implementation Roadmap."

Not all commands may be available in your Cisco IOS software release. For release information about a specific command, see the command reference documentation.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS and Catalyst OS software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Note Table 3 lists only the Cisco IOS software release that introduced support for a given feature in a given Cisco IOS software release train. Unless noted otherwise, subsequent releases of that Cisco IOS software release train also support that feature.

Table 3 Feature Information for Configuring Basic BGP

Feature Name

Releases

Feature Configuration Information

BGP Conditional Route Injection

12.2(4)T12.2(14)S12.0(22)S

The BGP Conditional Route Injection feature allows you to inject more specific prefixes into a BGP routing table over less specific prefixes that were selected through normal route aggregation. These more specific prefixes can be used to provide a finer granularity of traffic engineering or administrative control than is possible with aggregated routes.

The BGP Configuration Using Peer Templates feature introduces a new mechanism that groups distinct neighbor configurations for BGP neighbors that share policies. This type of policy configuration has been traditionally configured with BGP peer groups. However, peer groups have certain limitations because peer group configuration is bound to update grouping and specific session characteristics. Configuration templates provide an alternative to peer group configuration and overcome some of the limitations of peer groups.

The BGP Dynamic Update Peer Groups feature introduces a new algorithm that dynamically calculates and optimizes update groups of neighbors that share the same outbound policies and can share the same update messages. In previous versions of Cisco IOS software, BGP update messages were grouped based on peer-group configurations. This method of grouping updates limited outbound policies and specific-session configurations. The BGP Dynamic Update Peer Group feature separates update group replication from peer group configuration, which improves convergence time and flexibility of neighbor configuration.

The BGP Hybrid CLI feature simplifies the migration of BGP networks and existing configurations from the NLRI format to the AFI format. This new functionality allows the network operator to configure commands in the AFI format and save these command configurations to existing NLRI formatted configurations. The feature provides the network operator with the capability to take advantage of new features and provides support for migration from the NLRI format to the AFI format.

The BGP Neighbor Policy feature introduces new keywords to two existing commands to display information about local and inherited policies. When BGP neighbors use multiple levels of peer templates, it can be difficult to determine which policies are applied to the neighbor. Inherited policies are policies that the neighbor inherits from a peer-group or a peer-policy template.

The following commands were modified by this feature: show ip bgp neighbors, show ip bgp template peer-policy.

Suppress BGP Advertisement for Inactive Routes

12.2(25)S12.2(33)SXH

The Suppress BGP Advertisements for Inactive Routes feature allows you to configure the suppression of advertisements for routes that are not installed in the Routing Information Base (RIB). Configuring this feature allows Border Gateway Protocol (BGP) updates to be more consistent with data used for traffic forwarding.

Any Internet Protocol (IP) addresses used in this document are not intended to be actual addresses. Any examples, command display output, and figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses in illustrative content is unintentional and coincidental.